Network Working Group C.P. Pelsser Internet-Draft R.B. Bush Intended status: Standards Track Internet Initiative Japan Expires: September 12, 2013 K.P. Patel P.M. Mohapatra Cisco Systems O.M. Maennel Loughborough University March 11, 2013 Making Route Flap Damping Usable draft-ietf-idr-rfd-usable-02 Abstract Route Flap Damping (RFD) was first proposed to reduce BGP churn in routers. Unfortunately, RFD was found to severely penalize sites for being well-connected because topological richness amplifies the number of update messages exchanged. Many operators have turned RFD off. Based on experimental measurement, this document recommends adjusting a few RFD algorithmic constants and limits, to reduce the high risks with RFD, with the result being damping a non-trivial amount of long term churn without penalizing well-behaved prefixes' normal convergence process. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [RFC2119] only when they appear in all upper case. They may also appear in lower or mixed case as English words, without normative meaning. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Pelsser, et al. Expires September 12, 2013 [Page 1] Internet-Draft Making Route Flap Damping Usable March 2013 This Internet-Draft will expire on September 12, 2013. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Suggested Reading . . . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3. RFD Parameters . . . . . . . . . . . . . . . . . . . . . . . 3 4. Suppress Threshold Versus Churn . . . . . . . . . . . . . . . 3 5. Maximum Penalty . . . . . . . . . . . . . . . . . . . . . . . 4 6. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 10.1. Normative References . . . . . . . . . . . . . . . . . . 5 10.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Suggested Reading It is assumed that the reader understands BGP, [RFC4271] and Route Flap Damping, [RFC2439]. This work is based on the measurements in the paper [pelsser2011]. A survey of Japanese operators' use of RFD and their desires is reported in [I-D.shishio-grow-isp-rfd-implement-survey]. 2. Introduction Route Flap Damping (RFD) was first proposed (see [ripe178] and [RFC2439]) and subsequently implemented to reduce BGP churn in routers. Unfortunately, RFD was found to severely penalize sites for being well-connected because topological richness amplifies the number of update messages exchanged, see [mao2002]. Subsequently, Pelsser, et al. Expires September 12, 2013 [Page 2] Internet-Draft Making Route Flap Damping Usable March 2013 many operators turned RFD off, see [ripe378]. Based on the measurements of [pelsser2011], [ripe580] now recommends that RFD is usable with some changes to the parameters. Based on the same measurements, this document recommends adjusting a few RFD algorithmic constants and limits, with the result being damping of a non-trivial amount of long term churn without penalizing well-behaved prefixes' normal convergence process. Very few prefixes are responsible for a large amount of the BGP messages received by a router, see [huston2006] and [pelsser2011]. For example, the measurements in [pelsser2011] showed that only 3% of the prefixes were responsible for 36% percent of the BGP messages at a router with real feeds from a Tier-1 and an Internet Exchange Point during a one week experiment. Only these very frequently flapping prefixes should be damped. The values recommended in Section 6 achieve this. Thus, RFD can be enabled, and some churn reduced. The goal is to, with absolutely minimal change, ameliorate the danger of current RFD implementations and use. It is not a panacea, nor is it a deep and thorough approach to flap reduction. 3. RFD Parameters The following RFD parameters are common to all implementations. Some may be tuned by the operator, some not. +-------------------------+----------+-------+---------+ | Parameter | Tunable? | Cisco | Juniper | +-------------------------+----------+-------+---------+ | Withdrawal | No | 1000 | 1000 | | Re-Advertisement | No | 0 | 1000 | | Attribute Change | No | 500 | 500 | | Suppress Threshold | Yes | 2000 | 3000 | | Half-Life (min) | Yes | 15 | 15 | | Reuse Threshold | Yes | 750 | 750 | | Max Suppress Time (min) | Yes | 60 | 60 | +-------------------------+----------+-------+---------+ Default RFD Paramaters of Juniper and Cisco Table 1 4. Suppress Threshold Versus Churn By turning RFD back on with the values recommended in Section 6 churn is reduced. Moreover, with these values, prefixes going through normal convergence are generally not damped. Pelsser, et al. Expires September 12, 2013 [Page 3] Internet-Draft Making Route Flap Damping Usable March 2013 [pelsser2011] estimates that, with a suppress threshold of 6,000, the BGP update rate is reduced by 19% compared to a situation without RFD enabled. With this 6,000 suppress threshold, 90% fewer prefixes are damped compared to use of a 2,000 threshold. I.e. far fewer well- behaved prefixes are damped. Setting the suppress threshold to 12,000 leads to very few damped prefixes (1.7% of the prefixes damped with a threshold of 2,000, in the experiments in [pelsser2011] yielding an average hourly update reduction of 11% compared to not using RFD. +-----------------+-----------------+-------------+-----------------+ | Suppress | Damped | % of Table | Update Rate | | Threshold | Instances | Damped | (one hour bins) | +-----------------+-----------------+-------------+-----------------+ | 2,000 | 43342 | 13.16% | 53.11% | | 4,000 | 11253 | 3.42% | 74.16% | | 6,000 | 4352 | 1.32% | 81.03% | | 8,000 | 2104 | 0.64% | 84.85% | | 10,000 | 1286 | 0.39% | 87.12% | | 12,000 | 720 | 0.22% | 88.74% | | 14,000 | 504 | 0.15% | 89.97% | | 16,000 | 353 | 0.11% | 91.01% | | 18,000 | 311 | 0.09% | 91.88% | | 20,000 | 261 | 0.08% | 92.69% | +-----------------+-----------------+-------------+-----------------+ Damped Prefixes vs. Churn, from [pelsser2011]. Note overly- aggressive current default Suppress Threshold Table 2 5. Maximum Penalty It is important to understand that the parameters shown in Table 1, and the implementation's sampling rate, impose an upper bound on the penalty value, which we can call the 'computed maximum penalty'. In addition, BGP implementations have an internal constant which we will call the 'maximum penalty' which the current computed penalty may not exceed. 6. Recommendations The following changes are recommended: Router Maximum Penalty: The internal constant for the maximum penalty value MUST be raised to at least 50,000. Pelsser, et al. Expires September 12, 2013 [Page 4] Internet-Draft Making Route Flap Damping Usable March 2013 Default Configurable Parameters: In order not to break existing operational configurations, BGP implementations SHOULD NOT change the default values in Table 1. Minimum Suppress Threshold: Operators wishing damping which is much less destructive than current, but still somewhat aggressive SHOULD configure the Suppress Threshold to no less than 6,000. Conservative Suppress Threshold: Conservative operators SHOULD configure the Suppress Threshold to no less than 12,000. Calculate But Do Not Damp: Implementations MAY have a test mode where the operator could see the results of a particular configuration without actually damping any prefixes. This will allow for fine tuning of parameters without losing reachability. 7. Security Considerations It is well known that an attacker can generate false flapping to cause a victim's prefix(es) to be damped. As the recommendations merely change parameters to more conservative values, there should be no increase in risk. In fact, the parameter change to more conservative values should slightly mitigate the false flap attack. 8. IANA Considerations This document has no IANA Considerations. 9. Acknowledgments Nate Kushman initiated this work some years ago. Ron Bonica, Seiichi Kawamura, and Erik Muller contributed useful suggestions. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route Flap Damping", RFC 2439, November 1998. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. Pelsser, et al. Expires September 12, 2013 [Page 5] Internet-Draft Making Route Flap Damping Usable March 2013 [mao2002] Mao, Z. M., Govidan, R., Varghese, G., Katz, R., "Route Flap Damping Excacerbates Internet Routing Convergence", In Proceedings of SIGCOMM , August 2002, . [pelsser2011] Pelsser, C., Maennel, O., Mohapatra, P., Bush, R., Patel, K., "Route Flap Damping Made Usable", Passive and Active Measurement (PAM), March 2011, . [ripe378] Panigl, P. Smith, P., "RIPE Routing Working Group Recommendations On Route-flap Damping", 2006, . 10.2. Informative References [I-D.shishio-grow-isp-rfd-implement-survey] Tsuchiya, S., Kawamura, S., Bush, R., and C. Pelsser, "Route Flap Damping Deployment Status Survey", draft- shishio-grow-isp-rfd-implement-survey-05 (work in progress), June 2012. [huston2006] Huston, G., "BGP Extreme Routing Noise", RIPE 52 , 2006, . [ripe178] Barber, T., Doran, S., Karrenberg, D., Panigl, C., Schmitz, J., "RIPE Routing-WG Recommendation for Coordinated Route-flap Damping Parameters", 2001, . [ripe580] Pelsser, C., Bush, R., Maennel, O., Patel, K., Mohapatra, P., Kuhne, M., Evans, R., "RIPE Routing-WG Recommendation for Route-flap Damping", 2013, . Authors' Addresses Pelsser, et al. Expires September 12, 2013 [Page 6] Internet-Draft Making Route Flap Damping Usable March 2013 Cristel Pelsser Internet Initiative Japan Jinbocho Mitsui Buiding, 1-105 Kanda-Jinbocho, Chiyoda-ku, Tokyo 101-0051 JP Phone: +81 3 5205 6464 Email: cristel@iij.ad.jp Randy Bush Internet Initiative Japan 5147 Crystal Springs Bainbridge Island, Washington 98110 US Email: randy@psg.com Keyur Patel Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 US Email: keyupate@cisco.com Pradosh Mohapatra Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 US Email: pmohapat@cisco.com Olaf Maennel Loughborough University Department of Computer Science - N.2.03 Loughborough UK Phone: +44 115 714 0042 Email: o@maennel.net Pelsser, et al. Expires September 12, 2013 [Page 7]